The invention relates to a motor drive and control apparatus for a camera, and more particularly, to such apparatus which drives a driven member such as a taking lens or a photographic film used in an automatic focus adjusting unit or automatic film winding unit, respectively, through a given stroke toward a target position where it is stopped.
An automatic focus adjusting unit in which a taking lens is controlled to move to a target in-focus position has been proposed by the present applicant in Japanese Patent Application No. 302,692/1986, where a motor is controlled by comparing a deceleration curve against an actual speed of movement of a taking lens and in which a limited acceleration technique is employed as the taking lens approaches an in-focus position, by limiting an on time of the motor to a fixed time interval in order to prevent an overshooting which may result from the continued on condition of the motor. However, the limited acceleration takes place over a fixed time interval independently of the speed of movement of the taking lens which represents a driven member or the load, and hence it is inevitable that there occurs an over- or under-acceleration. In addition, the program used merely counts the length of time during which the motor is turned on, and hence it is impossible to sense a signal from a detector which detects a speed of movement, causing a likelihood that the speed of movement may be errorneously detected.
An automatic film winding unit in which a drive motor is stopped at a given winding step position is disclosed in Japanese Laid-Open Patent Application No. 24,123/1983. In this disclosure, a pulse which is developed in response to a movement of a film through a given stroke is utilized after the motor has entered a constant speed rotation to derive a speed of movement of a film which represents a driven member, and a brake is applied on the basis of an expected overrun which is derived from a previously stored table representing a relationship between the speed of movement of the film and the magnitude of overrun. However, because the application of the brake is based on the expected overrun, any variation in the load being wound up or drive voltage which might occur during the braking operation may cause a deviation between the expected and the actual overrun, resulting in a failure to stop the film winding operation at a target position. In addition, the relationship between the speed of movement of the film and the overrun may vary from product to product, involving the likelihood that a certain product may fail to stop the film at a target position.